On Friday afternoon, Google made the biggest change that has ever happened in search engines, and the world largely yawned. Maybe Google timed its announcement that it was personalizing everyone’s search results just right, so few would notice. Maybe no one really understood how significant the change was. Whatever the reason, it was a huge development and deserves much more attention than it has received so far.

Until now, search engines have largely delivered the same results to everyone. Two different people could search for Barack Obama and get back the same set of results. In fact, the results have been so consistent that people have used them as a universal navigation tool.

For example, Sony Pictures ran an ad campaign for its 2012 movie with the tagline “Search: 2012,” apparently guessing correctly that anyone searching for that word would find the movie web site. WordPress founder Matt Mullenweg has a business card that says to find him by searching for matt on Google.

The days of “normal” search results that everyone sees are now over. Personalized results are the “new normal,” and the change is going to shift the search world and society in general in unpredictable ways.

What are the results you get back for a search on the US health care debate? Fox News might be all set to lambaste Google for giving a liberal site top billing, only to find that CNN reports that it’s a conservative site that’s number one — and both stations might be wrong. That’s because the results each reports on will be only what their particular reporters at each station saw. Their viewers may see different results. In fact, each one of their viewers may see results different from one another.

Happy that you’re ranking in the top results for a term that’s important to you? Look again. Turn off personalized search, and you might discover that your top billing is due to the way the personalized system is a huge ego search reinforcement tool. If you visit your own site often, your own site ranks better in your own results — but not for everyone else.

Does this mean SEO is dead? No. I’ve warned for years that search results would be getting more personalized. Still, for many queries, there will continue to be “normal” results until Google harvests enough information to start personalizing them. SEO remains important to ensure that you’ve got that first shot at being considered. And the best tip in this new world of personalization remains the same. Make a good impression. Titles and descriptions are important, as is having outstanding content.

Are normal results really dead? They’ve actually been dying for some time, as Google has “group” personalized results on a country-by-country basis, then on a region-by-region basis. Those in the UK have long seen results slightly different than those in the US. Those in San Francisco have gotten results slightly different than those in Los Angeles. Some of this has been disclosed, as Google Now Notifies Of “Search Customization” & Gives Searchers Control from last year explains more.

Even with last week’s new universal personal results (now there’s an oxymoron!) rollout, where everyone is getting personalized results, there should remain many searches where two people can do the same query and get very similar to identical results. Personalization isn’t so dramatic that everyone will see radically different stuff. In particular, Google told me it doesn’t envision a future where someone who’s conservative would get only conservative results while someone who’s liberal will get only liberal ones:

“We want diversity of results,” said product manager Johanna Wright, when we talked about the personalized release on Friday. “This is something we talk about a lot internally and believe in. We want there to be variety of sources and opinions in the Google results. We want them in personalized search to be skewed to the user, but we don’t want that to mean the rest of the web is unavailable to them.”

Still, make no mistake. “Normal” is dead. This isn’t the personalized search system of old, where Google only personalized results if people were signed in. In the new personalized search, millions of Google users have been opted-in to the system even if they aren’t signed-in using a Google account. While people can opt-out of personalized results, I doubt many will do so. That also means SEOs shouldn’t get distracted wondering about hacks to view “normal” results. Even though the pws=0 technique still apparently works, it’s not like typical Google users are using it.

Should Google have required opt-in? I’m split. Last week, I was talking about personalized search in general to someone who was concerned that Google would make exactly this move, without asking. I explained that it’s a tough call. There’s some reasonable expectation that you can use what people have told you before.

Imagine you’re in a library — the classic metaphor for a search engine and how it interacts with a searcher, from when WebCrawler’s Brian Pinkerton used to explain how they worked back in the 1990s. Someone walks in and says “travel.” In a library, the librarian would ask more questions, to try and understand what they want. Early search engines didn’t do this. They couldn’t do this!

Over time, search engines tried to do the library-style conversation by offering related searches, as a way to get searchers to refine their queries. Then Google took a huge leap last year by making use of your previous query to refine your results. That makes sense and doesn’t seem to require any particular reason to ask for user opt-in. Again, imagine the librarian. It would be unreasonable to expect them to forget the last thing you said in a conversation you were having, as they tried to help you. Unreasonable and unhelpful.

But would you expect the librarian to help you by remembering everything you’d asked over a half-year period? That might be helpful, sure, but it might also be eerie. But this is what Google is doing now. It remembers everything you’ve searched for over 180 days, and it uses that information to customize your results. To alert you about this huge change, it made a blog post on Friday afternoon. That’s it.

This is the second time Google widely expanded personalized search on an opt-out, rather than an opt-in basis. Google Ramps Up Personalized Search covers how in 2007, Google enrolled anyone with a new Google Account into personalized search. At least then, it also showed a big notice on the search results page to alert you that personalization was happening. With Friday’s change, you have to spot the “Web History” link in the upper-right hand corner of search pages to understand logging is being used to customize your results. Or you have to spot the “View Customizations” link.

When Google can expend some of its precious home page space to shill its Android phones, it’s not unreasonable that it might consider alerting searchers to the personalized search change in this visible area. It’s not unreasonable that rather than immediately opting everyone in, it might have considered giving people 3 to 6 months notice that the change was going to happen.

Still, the shift deserves more attention than it received through a Friday afternoon rollout. The passing of old “normal” results deserves a better obituary than that. Attention must be paid. Searchers, site owners and others — take note.